Coin validator calibration

ABSTRACT

The coin validator is calibrated by inserting a calibration key different from coins to be validated in a static position in the validator such that eddy currents are induced in the key by operation of its sensor coils so as to produce a calibration value of signals form the sensor coils as a function of the individual characteristics of the validator. The calibrating value of the sensor signals may be compared with ensemble data concerning corresponding calibration values derived from an ensemble of coin validators of the same design.

FIELD OF THE INVENTION

This invention relates to calibrating coin validators in order to permiteach validator to be provided with accurate data concerning acceptablecoins, that can be compared with coin data derived from coins to bevalidated, in order to determine coin acceptability.

BACKGROUND

Coin validators which discriminate between coins of differentdenominations are well known and one example is described in our GB-A-2169 429. This coin validator includes a coin rundown path along whichcoins pass edgewise through a coin sensing station at which a series ofinductive tests are performed on the coins with sensor coils in order todevelop sensor signals which are indicative of the size and metalliccontent of the coin under test. The sensor signals are digitised so asto provide coin data, which are then compared with stored data by meansof a microprocessor to determine the acceptability or otherwise of thecoin under test. If the coin is found to be acceptable, themicroprocessor operates an accept gate so that the coin is directed toan accept path. Otherwise, the accept gate remains inoperative and thecoin is directed to a reject path.

The stored data are representative of acceptable values of the coindata. The stored data in theory could be represented by a single digitalvalue but in practice, the coin parameter data varies from coin to coin,due to differences in the coins themselves and consequently, it is usualto store the data as window data corresponding to windows or ranges ofacceptable values of the coin data.

The window data needs to vary from validator to validator due to minormanufacturing differences that occur between validators manufactured tothe same design. Consequently, it is not possible to program a fixed setof window data into mass produced coin validators of the same design. Aconventional solution to this problem is to calibrate the validatorsindividually by passing a series of known true coins of a particulardenomination through the validator so as to derive test data from whichappropriate window data can be computed and stored in the memory of thevalidator. Reference is directed to GB-A-1 452 740. This calibrationmethod is however, time consuming because a group of test coins for eachdenomination needs to be passed through the validator in order to derivedata from which the windows can be computed.

Another calibration method is described in EP-A-0 072 189. In thismethod, first and second tokens in the form of metal discs are passedthrough the validator and subject to the same inductive tests as coinsto be validated. The tokens are chosen to have different characteristicsto the coins to be validated. During set up of the validator, the tokensare passed sequentially through the inductive sensing station and theresultant data are then compared with standard values from whichcalibration factors are calculated. A series of standard acceptablevalues of the coin data are provided and the calibration factors areapplied to the standard data to derive suitable compensated values ofacceptable coin data to be stored in the memory of the individualvalidator being calibrated.

A calibration tool is disclosed in U.S. Pat. No. 5,495,931, which isinserted into the coin rundown path. The tool includes a coil which isenergisable to induce signals to the sensor coils which emulate a coinand can be used to calibrate the validator. Reference is also directedto EP-A-0 602 474 which discloses a calibration method that usescalibration discs, and a calibration algorithm in the form of a Taylorseries.

These prior methods suffer a number of disadvantages. The use ofcalibration discs has the disadvantage that the calibration data derivedfrom the inductive tests is produced in response to the disc rollingthrough the validator, which limits the accuracy that can be obtained.Furthermore, the standard values of true coins that are compensatedaccording to the calibration factors, are not necessarily accurate. Theactively energised calibration tool may not in practice provideconsistent results due to differences in inductive coupling, fromvalidator to validator.

The present invention seeks to overcome these problems.

SUMMARY OF THE INVENTION

According to the invention from a first aspect there is provided amethod of calibrating a coin validator that includes a path for coins tobe validated and at least one inductive sensor means for forming aninductive coupling with a coin as it passes along the path thereby toproduce a sensor signal to be compared with coin data for determiningauthenticity of the coin, the sensor signal being of a value dependentupon characteristics of the validator, comprising inserting acalibration key different from coins to be validated in a staticposition in the validator such that eddy currents are induced in the keyby operation of the sensor means, so as to produce a calibration valueof the sensor signal as a function of the individual characteristics ofthe validator.

By using a calibration key in a static position in the validator, a muchmore accurate calibration value of the sensor signal may be obtainedthan with moving calibration token used hitherto.

The key may then be removed in order to allow the validator to be usedfor coin validation of coins under test.

The validator may include a coin rundown path disposed between the sidewalls which are movable relative to one another, for example to allowcoins that have become jammed in the rundown path to be removed, and themethod according to the invention may include the steps of moving theside walls apart, inserting the calibration key into the rundown path ata predetermined location, closing the side walls, and then forming theinductive coupling with the key in order to derive the calibration valueof the coin signal.

The inductive sensor means may comprise a plurality of inductor coils sothat respective inductive couplings are formed between the coils and thekey. The shape of the key may be configured in order to optimise therespective inductive couplings. The coupling may be producedsequentially, for example by energising the coils sequentially so thatthe individual inductive couplings between the coils and the key can bemonitored.

In another aspect, the invention provides a method of calibrating a coinvalidator that includes a path for coins to be validated and at leastone inductive sensor means for forming an inductive coupling with a coinas it passes along the path thereby to produce a sensor signal to becompared with coin data for determining authenticity of the coin, thesensor signal being of a value dependent upon characteristics of thevalidator, comprising: inserting a calibration key different from coinsto be validated in a static position in the validator such as to producean inductive coupling with the sensor means, so as to produce acalibration value of the sensor signal as a function of the individualcharacteristics of the validator, comparing the calibration value of thesensor signal with ensemble data concerning corresponding calibrationvalues of the sensor signal derived from an ensemble of coin validatorsof said design, and determining, as a function of the comparison, forsaid validator being calibrated, a value of the sensor signalcorresponding to a particular coin denomination, that is compensated inrespect of the individual characteristics of the validator.

Data concerning the compensated value of the sensor signal may be storedin the validator being calibrated, for example in a semiconductormemory. The compensated value may be stored as window data correspondingto a window of acceptable values of the coin signal in order toaccommodate variations from coin to coin. Additionally, data concerningthe calibration value of the sensor signal may be stored in thevalidator to allow subsequent reprogramming. The validator can then bereprogrammed to accept different denominations of coins, and this can beachieved by computing a compensated value of a sensor signal for a coinof a different denomination by reference to the stored value of thecalibration signal and an ensemble average of the coin signal for thedifferent denomination. This can be carried out after manufacture, forexample in the field.

Alternatively, calibration can be achieved by providing a database ofvalidator data sets derived from an ensemble of coin validators of thesame design as the validator being calibrated, each data set comprisingsaid calibration value for a respective individual validator of theensemble and a value of the coin signal produced in response to a truecoin of a particular denomination of the is individual validator, andselecting at least one of the data sets in dependence upon a comparisonof the coin signal calibration value for the validator being calibratedwith the corresponding calibration values of the data sets.

More than one calibration value of the sensor signal for an individualvalidator may be derived by inserting a plurality of different ones ofsaid keys in the rundown path so as to form different inductivecouplings with the inductive means.

The invention also includes coin validator calibration apparatusincluding a coin validator that includes a path for coins to bevalidated and at least one inductive means for forming an inductivecoupling with a coin as it passes along the path thereby to produce asensor signal to be compared with coin data for determining authenticityof the coin, the sensor signal being of a value dependent uponcharacteristics of the validator, and a calibration key, different fromcoins to be validated, configured to be mountable in a static positionin the validator such that eddy currents are induced in the key byoperation of the inductor means, so as to produce a calibration value ofthe sensor signal as a function of the individual characteristics of thevalidator.

Preferably, the calibration key is of a shape which self-locates in therundown path at a predetermined location. Alternatively, the key can beinserted into a carrier which is inserted into the coin path. Thevalidator may include a door which is openable to allow the key to beinserted at the predetermined location, so as to form the inductivecoupling with the inductive means, and thereafter removed, prior to useof the validator for coin validation.

The invention also extends to a method of calibrating a coin validatorof a predetermined design that includes a path for coins to be validatedand at least one inductive sensor means for forming an inductivecoupling with a coin as it passes along the path thereby to produce asensor signal to be compared with coin data for determining authenticityof the coin, the sensor signal being of a value dependent uponcharacteristics which may vary from validator to validator, comprisingforming a calibration inductive coupling with the inductive meanswhereby to produce a calibration value of the sensor signal as afunction of individual characteristics of the validator, comparing thecalibration value of the sensor signal with data concerningcorresponding calibration values of the sensor signal derived from anensemble of coin validators of said design and sensor signals producedby the validators of the ensemble in response to a true coin of aparticular denomination, such as to derive for the validator beingcalibrated a value of the sensor signal for said denomination, that iscompensated in respect of the individual characteristics of thevalidator, the calibration value of the sensor signal being comparedwith data from a database of validator data sets derived from saidensemble of coin validators of said design, each set comprising saidcalibration value for a respective individual validator of the ensembleand a value of the sensor signal produced in response to a true coin ofa particular denomination by the individual validator.

Data may be selected from the data sets in dependence upon a comparisonof the sensor signal calibration value for the validator beingcalibrated, with the corresponding calibration values of the data sets.

A plurality of average values of the difference between the calibrationvalue of the sensor signal and the corresponding sensor value for thetrue coin, may be formed from the data sets, for the data sets in whichthe calibration value of the sensor signal falls within predeterminedrespective ranges of values thereof. Data concerning said ranges and theaverage values can be transmitted to the coin validator to becalibrated, and one of said ranges may then be selected by comparing thecalibration value of the sensor signal for the validator beingcalibrated, with said ranges, and the average value for the selectedrange may be combined with the calibration value of the sensor signalfor the validator being calibrated, so as to provide the compensatedvalue of the sensor signal for the validator being calibrated. Thetransmitted data may be fed from a is central location to a plurality ofvalidators to be calibrated at remote locations, or to individualvalidators in response to a request from the validator location.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully understood embodimentsthereof will now be described by way of example with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic elevational view of a coin rundown path through acoin validator to be calibrated in accordance with the invention, withits reject gate not shown;

FIG. 2 is an elevational view of the validator shown in FIG. 1, from oneside, showing the reject gate;

FIG. 3 is a top plan view of the validator shown in FIG. 2;

FIG. 4 is a partial schematic sectional view taken along the line A—A′shown in FIG. 2;

FIG. 5 illustrates schematically electrical circuits of the validator;

FIG. 6 is a schematic block diagram of the main process steps performedto calibrate the coin validator;

FIG. 7 is a schematic side view of a calibration key for use in a methodaccording to the invention;

FIG. 8 is a schematic elevational view of the validator shown in FIG. 2illustrating the calibration key in situ;

FIG. 9 is a more detailed flow diagram of the steps performed during theensemble data collection shown in FIG. 6;

FIG. 10 illustrates in more detail one example of the characterisationstep shown in FIG. 6;

FIG. 11 is a graph of the relationship between the ensemble averages ofthe calibration values of the coin signal derived from the calibrationkeys and a true coin (x-axis), with the corresponding individual valuesfor a validator being calibrated (y-axis);

FIG. 12 illustrates in more detail one example of the dedication stepshown in FIG. 6, for use with the characterisation steps described withreference to FIG. 10;

FIG. 13 is a graph illustrating a database of set of coin signalsderived for a plurality of different test true coins and two calibrationkeys (y-axis) derived from a plurality (n) of coin validators in anensemble thereof (x-axis) for use in a second example of the method ofthe invention;

FIG. 14 illustrates a second example of the characterisation step ofFIG. 6, for use with the database shown in FIG. 13;

FIG. 15 illustrates a second example of the dedication step of FIG. 6,for use with the characterisation process described with reference toFIG. 14; and

FIG. 16 is a schematic flow diagram of a third example of a methodaccording to the invention, in which calibration data is transmitted tovalidators at remote locations from a central database.

DETAILED DESCRIPTION

Referring to FIG. 1, a coin validator consists of a body 1 including acoin inlet 2 into which coins are inserted from above so as to fall ontoan inclined coin rundown surface 3 and then roll edgewise through aninductive coin sensing station 4 which includes sensing coils C1, C2,and C3 shown in dotted outline. A coin 5 is shown on the inclinedrundown surface 3, which moves along a path 6 shown in dotted outline.

At the end of the inclined rundown surface 3, the coin falls through anopening 7 towards the solenoid operated accept gate 8 that either allowsthe coin to enter an accept path 9 or directs the coin along a rejectpath 10. The accept gate is operated by circuitry responsive to theinductive sensing coils C1-3 at the sensing station 4 so that if thecoin is determined to be of acceptable characteristics, the gate 8 isopened by a sliding operation normal to the plane of the paper in FIG.1, so that the coin can fall along path 9 and be accepted. The passageof the coin into the accept path may be directed by a further sensor(not shown). Otherwise, the gate 8 remains closed so as Is to block theaccept path and as a result, the coin is deflected by the gate into thereject path 10.

The coin 5 runs in a gap between opposed side walls which, as can beseen in FIGS. 2, 3 and 4, are defined by a wall 11 on the body 1 of thevalidator and an interior wall 12 of a rundown gate 13 which is hingedabout a substantially vertical axis on a shaft 14 mounted on the body 1.The main rundown surface 3 comprises a ledge formed on the bottom edgeof the rundown gate 13 (FIG. 4). The rundown gate 13 is normally biassedto a closed position by springs 15 so that the walls 11, 12 aregenerally parallel to one another as shown in hatched outline in FIG. 3.However, the rundown gate 13 can be hinged outwardly as shown in solidoutline in FIG. 3, by operation of a reject lever in a manner known perse in order to release coins in the rundown path, in the event of a coinjam. Also, the gate 13 can be opened further in order to provide accessto the rundown path as will be explained in more detail hereinafter.

The three sensing coil circuits C1-3 at the coin sensing station 4 shownin FIG. 1, are mounted in the validator body. Each circuit comprises apair of coils connected in series on opposite sides of the coin rundownpath, one of the coins being mounted behind the wall 11 and the other inthe rundown gate 13, and they are energised in order to provide aninductive coupling with the coin that runs along the coin rundown path3. The coils are of different geometrical configurations and areenergised at different frequencies by a drive and interface circuit 16shown in FIG. 5 mounted in the validator body. The different inductivecouplings between the three coils and the coin have been found tocharacterise the coin substantially uniquely, in terms of its metalliccontent and physical dimensions. The drive and interface circuit 16produces three corresponding sensor signals x₁, x₂, x₃ as a function ofthe different inductive couplings between the coin 5 and the coils C1-3.The sensor signals x₁, x_(2, x) ₃ can be formed in a number of differentknown ways. One way is described in detail in our GB-A-2 169 429. Inthis method, the coils are included in individual resonant circuitswhich are maintained at their natural resonant frequency as the coinpasses the coil. The frequency changes on a transitory basis as a resultof the momentary change in impedance of the coil produced by theinductive coupling with the coin. This change in impedance produces achange both in amplitude and frequency. As described in our priorspecification, the peak amplitude deviation is monitored as the coinpasses the coils, and is digitised in order to provide the sensor signalx for each coil circuit. By maintaining the drive frequency for the coilcircuit at its natural resonant frequency during passage of the coinpast the coil, the amplitude deviation is emphasised so as to aid indiscrimination between coins. However, the signals can be formed inother ways, for example by monitoring the frequency produced as the coinpasses the coils and reference is directed to GB-A-1 452 740, or bymonitoring phase changes as a coin passes the coils.

In order to determine coin authenticity, the three sensor signals x₁,x₂, x₃ produced by the coin under test are fed to a microprocessor 17which is coupled to memory means in the form of an EEPROM 18 in thevalidator.

The microprocessor 17 compares the sensor signals derived from the coinunder test with corresponding stored values held in the EEPROM 18. Thestored values are stored in terms of windows having upper and lowerlimits. Thus, if the individual sensor signals x₁, x₂, x₃ fall withinthe corresponding windows associated with a true coin of a particulardenomination, the coin is considered to be acceptable, but otherwise isrejected. If acceptable, a signal is provided on line 19 to a drivecircuit 20 which operates the gate 8 shown in FIG. 1 so as to allow thecoin to pass to the accept path 9. Otherwise, the gate is not opened andthe coin passes to the reject path 10. During the coin validationprocess, the microprocessor compares the sensor signals x₁, x₂ and x₃with a number of different sets of operating window data appropriate forcoins of different denominations so that the coin validator can acceptor reject more than one coin of a particular currency set.

The present invention is concerned with providing the stored data in thememory 18 of the validator that can be used for comparison purposes withthe coin parameter signals derived from coins under test. Validatorsthat are mass produced to the same design do not have exactly the samecharacteristics as a result of manufacturing tolerances. Consequently,the value of the data stored in the EEPROM 18 needs to be slightlydifferent from validator to validator in order to optimise coindiscrirmination between coins of different denominations. The presentinvention is concerned with optimising the values of the stored data inorder to compensate for individual differences in the characteristics ofthe validators, which occur from validator to validator.

Examples of the calibration process according to the invention will nowbe described. In the following examples, calibration values of theindividual sensor signals x₁, x₂, X₃ are derived from an individualvalidator during a calibration procedure and the resulting calibrationvalues of the sensor signals are then compared with similar signalsderived from an ensemble of coin validators manufactured to the samedesign as the validator being calibrated. This enables thecharacteristics of the individual validator to be determined so thatcoin parameter data representative of acceptable coins can be suitablyprogrammed into the validator, taking account of its individualcharacteristics.

The calibration process can be considered to consist of three majorsteps as shown in FIG. 6. In the first step S1, an ensemble of data iscollected concerning the characteristics of an ensemble of coinvalidators all manufactured to the same design. At step S2, anindividual validator to be calibrated, is characterised with referenceto the ensemble data collected at step S1. At step S3, the individualvalidator is dedicated with coin parameter the reference datarepresentative of acceptable coins of different denominations, thereference data having been selected in dependence upon the result of thecharacterisation step S2. Three main different characterisation anddedication methods will be described in detail hereinafter.

In the following examples, the ensemble data collection step S1 and thecharacterisation step S2 both make use of a calibration key K and anexample is shown in FIG. 7.

The key consists of a metal plate, typically made of brass or some othersuitable alloy such as nickel copper, in order to produce a particularinductive coupling with the coils C1, C2 and C3 at the sensing station 4shown in FIG. 1. The calibration key K is inserted into the validator ata fixed, static position as shown in FIG. 8. The key K is inserted intothe validator by opening the rundown door 13 and placing the key on thecoin rundown path. The key K is configured so that it self-aligns at aparticular location. It includes a pin P which locates in a recess R inthe rundown door 13. This can be seen in FIG. 8. The key has aperipheral configuration which completely overlies the diameter of coilC3 and partially obscures coil C1 and C2. Thus, different inductivecouplings are formed with the coils C1, C2 and C3 individually. The keyK thus provides a reference against which the validator can becalibrated in terms of the inductive coupling of the sensor coils C1-C3.The reference is different from the inductive couplings produced bycoins under test. As will be apparent hereinafter, keys of differentmaterials and/or shapes may be used in the method according to theinvention to produce different sets of calibration values of the sensorsignals. Also, instead of self-locating in the rundown path, the key maybe inserted in a key carrier (not shown), which itself is inserted intothe path to locate the key in place next to the coils C1-3.

The data collection step S1 for the ensemble of coin validators will nowbe described with reference to FIG. 9. At step S1.1 the first validatorof the ensemble is connected to an external processor 22 (shown in FIG.5) such as a personal computer, by means of a connection 21 (FIGS. 5 and8) to the bus of the microprocessor 17. Then at step S1.2, a firstcalibration key K₁ is inserted in the coin rundown path in the mannershown in FIG. 8. The sensor coil circuits C1, C2 and C3 are sequentiallyenergised, one at a time, by the driver circuit 16 shown in FIG. 5 so asto produce sequential calibration values of the sensor signals x₁, x₂,X₃. It will be understood that these signals are digital. Because thekey is located in a static position, the coil circuits can be energisedfor a longer period than for a coin rolling along the rundown path,permitting highly accurate calibration values to be obtained. Themicroprocessor 17 is configured to send the calibration values to theexternal processor 22, where they are stored.

At step S1.3, the first key K₁ is replaced by a second calibration keyK₂ which may be made of a different material and/or which is of adifferent shape, so as to produce a second, different set of inductivecouplings with the coils C1, C2, C3. The energisation process isrepeated and the calibration values of the coin signals for the secondkey are similarly stored in the external processor.

Then the key K₂ is removed and, at step S1.4, a set of known true coinsof a particular denomination, is fed into the validator. The values ofthe sensor signals x₁, x₂, x₃ produced by the known true coin aredirected by the microprocessor 17 to the external processor 22, wherethey are averaged for each signal x₁, x₂, x₃, and the average values arestored.

At step S1.5, the process is repeated until sets of data have beencollected from all of the coin validators in the ensemble. The ensemblemay typically comprise 50-200 validators.

When all of the data has been collected from the validators of theensemble, it is processed at step S1.6 in the external processor 22.

In the first example of the invention, an average value of the dataproduced for each of the coils is produced for the ensemble ofvalidators. The data received from the coils C1, C2 and C3 for theensemble of validators is considered separately. In this example, theoutputs from the coils C1 will be considered and it will be understoodthat the outputs from coils C2 and C3 is are processed in a similar way.Firstly, an ensemble average value k_(av) is produced for the values ofthe sensor signal x₁ produced by the validators of the ensemble inresponse to the first calibration key K₁. A similar signal k_(av) isproduced from the calibration values of x₁ produced in response to thesecond calibration key K₂ for the ensemble. Additionally, an averageensemble value t_(av) is produced for the stored value of the sensorsignal x₁ produced in response to the true coin introduced at step S1.4.Thus, the end of step S1.6 (FIG. 9) ensemble averages k1 _(av), k2 _(av)and t_(av) are produced in respect of each of the coils C1, C2, and C3respectively, which are stored in the external processor 22. This datacan then be used in a process which allows individual validators to becharacterised as they are manufactured, at step S2 of FIG. 6. This stepwill now be described in more detail with reference to FIG. 10.

Step S2.0, denotes the start of a procedure in which a newlymanufactured validator from the production line is characterised inrespect of its individual characteristics that result from manufacturingtolerances during the production process. At step S2:1 the validator isconnected to the external processor 22 in the manner shown in FIG. 5 anda first key K1 is inserted into the coin rundown path of the validatoras shown in FIG. 8. The key K1 is of the same design as the key K₁ thatwas used during the data collection process of FIG. 9 and hence has thesame key characteristics. At step S2.2, the sensor signals x₁, x₂, X₃are measured to provide individual calibration values Ik1 for thevalidator. The calibration value Ik1 for each coil circuit C1-C3 is thenstored in the external processor 22.

At step S2.3, the process is repeated in respect of the second key K₂that was used during the data collection process of FIG. 9, namely witha second key K2 with the same characteristic as K₂. The resultant coincalibration value Ik2 for each of the coils is stored in the externalprocessor 22.

When both of the keys have been inserted and removed from the validator,the process moves to step S2.4 at which the individual values Ik1 andIk2 are compared with the corresponding average values k1 _(av) and k2_(av). Referring to FIG. 11, it has been found according to theinvention that a plot of the calibration values Ik1, Ik2 against thecorresponding average values k1 _(av) and k2 _(av) approximates to astraight line when considering one of the sensor coil circuits e.g.sensor coil circuit C1. If additional different calibration keys areused, the average values kn_(av) and the corresponding individual valuesIkn lie on the same straight line. Similarly, the value t_(av) and acorresponding individual value It for a true coin fall on the samestraight line. Thus, by referencing the value t_(av) to the graph shownin FIG. 11 (on the x axis) it is possible to read off from the graph (onthe y axis) an individual true value for the particular coindenomination, for the individual validator being calibrated.

In this example of the invention, data concerning the slope andintercept of the graph shown in FIG. 11 is stored in the individualvalidator. It will be understood that the straight line graph shown inFIG. 11 is of the form

y=mx+c

where m is the gradient and c is y axis intercept and so from the valuesIk1 and Ik2 derived from the individual validator to be calibrated,together with the average values k1 _(av) and k2 _(av) it is possible tocompute the value of the intercept c and the slope m of the graph. Thevalues in and c are computed by the external processor 22, using thedata collected during steps S1 and step S2.2, at step S2.4 shown in FIG.10 and then, at step S2.5, the values of m and c are stored in thememory 18 of the individual validator being calibrated. Correspondingvalues of in and c for each of the sensor coil circuits C1, C2 and C3are stored in the memory 18.

Thereafter, the individual validator is dedicated to accept true coinsof a number of different denominations (step S3 of FIG. 6) which willnow be described in detail with reference to FIG. 12.

At step S3.0, the external processor 22 is connected to an individualvalidator and at step S3.1, the slope and intercept parameters m and care read from the memory 18 of the validator for each of the coilcircuits C1, C2 and C3. At step S3.2, the straight line graph of FIG. 11is effectively reconstructed by the processor 22 and then the previouslycomputed average value t_(av) for a true coin is interpolated so as toderive an individual true value for the validator concerned. This can beunderstood by referring to FIG. 11. An individual true value It for thevalidator can be determined from the y axis of the graph, at the pointof intersection of the x-ordinate value t_(av) and the line of thegraph. It will be understood that the processor 22 can readily computethis value from the value t_(av) and the retrieved values of m and c,for each of the sensor coil circuits C1, C2 and C3 respectively. Theresulting individual values It for the three coil circuits C1, C2 and C3are then stored in the memory 18 of the validator, at step S3.3. Infact, as previously mentioned, the individual values are stored aswindows with upper and lower limits disposed above and below the valueIt, in order to provide an acceptance window to take account ofdifferences in the coin signals produced by different true coins of thesame denomination, which in practice are found to occur from coin tocoin.

The validator is then ready for operation and the stored windows can becompared with the sensor signals X₁, x₂, and x₃ produced by coins undertest that pass through the validator.

It will be understood that during the data collection step of S1,appropriate mean values for a number of different true coins can beproduced by feeding a set of coins of different denominations througheach of the validators of the ensemble and producing correspondingaverages; step S1.4 can be repeated for different true coins, so thatduring the dedication step S3, the routine S3.3 can be repeated fordifferent true coins, to enable windows for true coins of differentdenominations to be stored in the memory of the validator, to allow itto validate a number of different coin denominations.

It is not necessary to program acceptance windows for all of the truecoins at the time of manufacture. It is possible to repeat thededication step S3, later, in the field if necessary, in order to changethe coin denominations to be accepted by the validator. To this end, theexternal processor 22 is connected to the validator, the stored valuesof m and c are extracted at step S3.1 and then, at step S3.2, newindividual values It are computed as previously described, using valuest_(av) appropriate for new acceptable coins for the validator.

In a second example of the calibration process, instead of forming theaverage values k_(av) and t_(2av) a database of validator data sets arederived from the ensemble of coin validators in the data collection stepS1. Each data set consists of the calibration value produced in responseto at least one of the keys K₁ or K₂ and a number of true coins T_(n)that are passed through each validator of the ensemble. Thus, each dataset comprises typically values k1, k2 of the sensor signal together withvalues t1, t2, t3 and t4 produced in response to corresponding truecoins T1, T2, T3 and T4 passed through the validator. Typically, 50-200such data sets are produced from the validators of the ensemble and acorresponding plot of the data is shown in FIG. 13.

During the characterisation step S2, data concerning the calibrationvalues of the sensor signal for the two keys K1 and K2, namely Ik1 and1k2 are stored in the memory 18 of the individual validator. Thisprocess is shown in FIG. 14 in which steps S2.1 to step S2.3 areperformed as previously described and then the resulting values Ik1 andIk2 are stored in the memory 18 of the validator being calibrated.

The dedication process is shown in FIG. 15. With the external processor22 connected to the validator, the key parameters Ik1, Ik2 are extractedfrom the memory 18 of the vaiidator at step S3.5, and then at step S3.6,these values are compared with the stored data sets that were collectedduring step S1. The two values Ik1 and Ik2 are compared with the valuesof the data sets from the ensemble thereof in order to choose the setwhich most closely resembles the key values stored in the validator. Inthis way, a data set is chosen which most closely approximates to thecharacteristics of the validator being dedicated. In a modification, anumber of the data sets from the ensemble may be chosen and the valuesthereof averaged, to reduce errors in the data.

Then, appropriate true coin values e.g t1, t2, t3 can be programmed intothe memory 18 of the individual validator, depending on which coins itis desired to validate. As previously described, windows may beassociated with each stored value in order to accommodate thedifferences in signals that occur for different true coins of the samedenomination.

In a third example of a method according to the invention, theinformation held in the database shown in FIG. 13 is rearranged to allowselective reprogramming of validators in the field, for example bytransmitting appropriate reprogramming data over a telephone line fromthe central station to the validator. It is assumed that the validatorhas in its memory a key parameter Ik1 and that its microprocessorincludes a reprogramming sub-routine which can operate at the validatoritself, rather than using an external processor such as processor 22.

The information concerning the database of FIG. 13 is held at a centrallocation for transmission to validators in the field. The database isorganised in such a way that the information can be readily transmittedto the validator.

In this example, it is assumed that the validator has already beenprogrammed s with appropriate true coin values for coins t1, t2 and t3in the manner described previously with reference to FIG. 15, and thatsubsequently, it is desired to program a value t4 for an additional truecoin. To achieve this, the database of FIG. 13 is reorganised such thatthe values of t4 for each data set are considered as a differencerelative to the value k1 for the set. Thus, for each data set, the valueof t4 can be written as follows:

t4=k1+Δ

It will be understood that the individual values of t4, k1 and Δ can bedifferent in each data set. The data of FIG. 13 is reorganised so as toprovide a series of “data bins” into which values of k1 betweenindividual is ranges are collected. This is shown as step S4.1 in FIG.16. It will be understood that the values of various parameters can beconsidered as count values as a result of the digital nature of thesignals. In the following Table, three data bins are shown by way ofexample, for count values of k between 100.00-100.99; 101.00-101.99 and102.00-102.99 although in practice, many more are used.

TABLE parameter bin 1 bin 2 bin 3 k1 100.00-100.99 101.00-101.99102.00-102.99 Δ_(2V) 10.25 10.27 10.24

The various values of the data sets are collected into the bins fordifferent values of k and at step S4.2, the values of Δ corresponding tothe data sets for each bin are averaged so as to form a value Δ_(av).The resulting values of the data bins and corresponding values of Δ_(av)are then stored in a memory at the central location.

When it is desired to program the value of t4 into the memory of avalidator at a remote location, the bin data as shown in the Table istransmitted digitally over a telephone line to the validator. Forexample, the validator can be considered to be at a remote locationrelative to the processor 22 of FIG. 5, e.g. in a pay telephone. Theprocessor 22 stores the bin data shown in the foregoing Table, and isconnected via a telephone line to the bus of the microprocessor 17through interface circuitry (not shown). After an initial handshakeprocedure, the validator switches to a calibration mode and dataconcerning the ranges of values of k1 for the successive data bins,together with the associated values of Δ_(av) are transmitted to thevalidator from the processor 22, as shown at step S4.3. The validatorretrieves its stored value of Ik1 and at step S4.5, notes when a binwhich contains the value is received from the central location. Thecorresponding value of Δ_(av) for the selected bin is added at step S4.5to the stored value of Ik1 so as to produce an appropriate value of t4for the validator. Appropriate window values are computed around thevalue of t4 and the resulting upper and lower window limits are storedin the memory 18 of the validator. It will be understood that inpractice bin data for more than one calibration key will be used.

It will be appreciated that this procedure permits selectivereprogramming of the memory 18 in the field either to change the valuesassociated with particular coins or to provide data for a new coindenomination. It will be understood that the data of the Table may bebroadcast to a plurality of validators in the field simultaneously, inorder that they may be reprogrammed simultaneously, without the need toextract their individual calibration values for external processing.Alternatively, the data of the Table may be transmitted to eachvalidator individually in response to a request received from thevalidator. For example, for a coin validator in a telephone coin box,when a new validator is fitted, it may be programmed by the downloadingthe Table data through the telephone system to the coin box, from aremote location, the downloading being initiated by a request from thecoin box control circuitry, in response to detection that a newvalidator has been fitted, e.g. in the event of a repair.

It has been found that the use of static calibration keys K has theadvantage that the count values of the sensor signal that are producedhave an improved accuracy as compared with the prior art arrangementswhich use tokens or coins which pass on a transitory basis past thecoils C1, C2, C3. Also, it has been found that the use of data from anensemble of coin validators gives a very accurate correlation betweenthe individual value stored in the memory of a validator, for anacceptable coin, and the actual value needed to achieve acceptable coindiscrimination. The use of the ensemble data has the advantage that itis no longer necessary to pass large numbers of coins of differentdenominations through each validator during manufacture, to calibrateits memory. Furthermore, the method may provide data stored in thememory of each validator which permits accurate reprogranming if it isdesired to use the validator with a different currency set.

In practice there may be more than one production line for validators ofthe same design, so that it would be desirable to have more than one setof keys for calibration purposes. However, the keys need to havedemonstrably identical characteristics, from set to set, in order toproduce consistent calibration. In order to meet this requirement, thecharacteristics of the keys can be compared relative to a master key, interms of the values x₁, x₂ and x₃ that they produce in an individualvalidator, and the difference between the value of say x₁, for one ofthe keys and a corresponding master key, can be stored in associationwith the key, and used as an offset in the actual calibration process.

Whilst the use of static keys is advantageous, it is possible to performthe method according to the invention by replacing the static key withknown true coins which function as mobile calibration keys that are fedthrough the validator in the same manner as the coin being validated.For the second example described with reference to FIGS. 13 to 15, thevalues of known true coins T1 and T2 could be used for characterisingthe validator at step S2 (FIG. 14) and the values thereof could becompared with the values in the database during the dedication step S3(FIG. 15).

The term “coin” herein includes a token or similar coin-like item ofvalue.

What is claimed is:
 1. A method of producing a calibration value for acoin validator that includes a path for coins to be validated and atleast one inductive sensor for forming an inductive coupling with a coinas it passes along the path thereby to produce a sensor signal to becompared with coin data for determining authenticity of the coin, thesensor signal being of a value dependent upon characteristics of thevalidator, comprising: inserting a calibration key different from coinsto be validated in a static position in the validator, and operating thesensor so that eddy currents are induced in the key, resulting in theproduction of the calibration value of the sensor signal as a functionof the individual characteristics of the validator.
 2. A methodaccording to claim 1 including associating upper and lower window limitvalues with the compensated value and storing the window limit values inthe validator being calibrated.
 3. A method according to claim 1including sequentially inserting a plurality of different ones of saidkeys in the rundown path for forming different inductive couplings withthe inductive sensor.
 4. A method according to claim 1 includingremoving the key from the validator prior to use thereof for validatingcoins under test.
 5. A method according to claim 1 wherein the path isdisposed between sidewalls which are movable relative to one another,including moving the sidewalls apart, inserting the calibration key intothe rundown path at a predetermined location, closing the sidewalls, andthen forming said inductive coupling with the key.
 6. A method accordingto claim 1 wherein the inductive sensor includes a plurality of inductorcoils, and respective inductive couplings are formed between the coilsand the key.
 7. A method according to claim 6 wherein said couplings areproduced sequentially.
 8. A method according to claim 7 includingenergising the coils sequentially and monitoring the inductive couplingbetween the coils and the key.
 9. A method according to claim 8 whereineach coil is connected in a circuit energised so that at least one ofthe phase, frequency and amplitude of the signal developed therebyvaries in response to insertion of the calibration key.
 10. A methodaccording to claim 9 wherein each coil is connected in a respectiveresonant circuit energised in such a manner as to maintain the circuitat its natural resonant frequency when a coin to be validated passes thecoil and when the calibration key is inserted, the method includingmonitoring the deviation in amplitude of the signal produced in theresonant circuit in response to insertion of the calibration key,whereby to produce the calibration signal.
 11. A method of providingdata for calibrating a coin validator that includes a path for coins tobe validated and at least one inductive sensor for forming an inductivecoupling with a coin as it passes along the path thereby to produce asensor signal to be compared with coin data for determining authenticityof the coin, the sensor signal being of a value dependent uponcharacteristics of the validator, comprising: inserting a calibrationkey different from coins to be validated in a static position in thevalidator, operating the sensor so as to produce an inductive couplingwith the calibration key and thereby producing a calibration value ofthe sensor signal as a function of the individual characteristics of thevalidator, comparing the calibration value of the sensor signal withensemble data concerning corresponding calibration values of the sensorsignal derived from an ensemble of coin validators of said design, anddetermining as a function of the comparison, for said validator beingcalibrated, data corresponding to the value of the sensor signal for aparticular coin denomination, that is compensated in respect of theindividual characteristics of the validator.
 12. A method according toclaim 11 wherein the ensemble data includes said data concerningcorresponding calibration values of the sensor signal derived from anensemble of coin validators of said design and data concerning sensorsignals produced by validators of the ensemble in response to a truecoin of said particular denomination.
 13. A method according to claim 12wherein the calibration value of the sensor signal is compared withensemble data comprising an ensemble average of correspondingcalibration values of the sensor signal derived from said ensemble ofcoin validators of said design and an ensemble average of sensor signalsproduced in response to a true coin of a particular denomination such asto derive said compensated value of the sensor signal for saiddenomination for said validator being calibrated.
 14. A method accordingto claim 1, including storing data concerning the compensated value ofthe sensor signal in the validator being calibrated.
 15. A methodaccording to claim 11, including storing data concerning the calibrationvalue of the sensor signal in the validator.
 16. A method according toclaim 15 including subsequently computing a compensated value of thesensor signal for a coin of a different denomination by reference tosaid stored value of the calibration signal and an ensemble average ofthe sensor signal for the different denomination.
 17. A method accordingto claim 11 wherein the calibration value of the sensor signal iscompared with data from a database of validator data sets derived fromsaid ensemble of coin validators of said design, each set comprisingsaid calibration value for a respective individual validator of theensemble and a value of the sensor signal produced in response to a truecoin of a particular denomination by the individual validator.
 18. Amethod according to claim 17 including selecting data from the data setsin dependence upon a comparison of the sensor signal calibration valuefor the validator being calibrated, with the corresponding calibrationvalues of the data sets.
 19. A method according to claim 17 includingforming from the data sets, a plurality of average values of thedifference between the calibration value of the sensor signal and thecorresponding sensor signal value for the true coin, for the data setsin which the calibration value of the sensor signal falls withinpredetermined respective ranges of values thereof.
 20. A methodaccording to claim 19 including transmitting data concerning said rangesand the average values to the coin validator to be calibrated, selectingone of said ranges by comparing the calibration value of the sensorsignal for the validator being calibrated with said ranges, andcombining said average value for the selected range with the calibrationvalue of the sensor signal for the validator being calibrated whereby toprovide the compensated value of the sensor signal for the validatorbeing calibrated.
 21. A method according to claim 20 wherein thetransmitted data is fed from a central location to a plurality ofvalidators to be calibrated at remote locations.
 22. Coin validatorcalibration apparatus including a coin validator that includes a pathfor coins to be validated and at least one inductor to form an inductivecoupling with a coin as it passes along the path thereby to produce asensor signal to be compared with coin data to determine authenticity ofthe coin, the sensor signal being of a value dependent uponcharacteristics of the validator, and a calibration key, different fromcoins to be validated, configured to be mountable in a static positionin the validator such that eddy currents are induced in the key byoperation of the inductor, so as to produce a calibration value of thesensor signal as a function of the individual characteristics of thevalidator.
 23. Coin validator calibration apparatus according to claim22 wherein the key is of a shape which self-locates in the path at apredetermined location.
 24. Coin validator calibration according toclaim 22 wherein the key includes a pin that is received in acorresponding recess in the coin rundown path.
 25. Coin validatorcalibration apparatus according to claim 22 including a carrier for thekey, to be removably fitted in the validator.
 26. Coin validatorcalibration apparatus according to claim 22 including a plurality ofsaid keys for forming different inductive couplings with the inductor.27. Coin validator calibration apparatus according to claim 22 whereinthe inductor comprises a plurality of coils at spaced locations relativeto the coin path, and the key is configured to produce differentrespective inductive couplings with the coils.
 28. Coin validatorcalibration apparatus according to claim 27 wherein the key comprises ametal plate.
 29. A method of producing a calibration value for a coinvalidator to be calibrated, the validator being of a predetermineddesign that includes a path for coins to be validated and at least oneinductive sensor for forming an inductive coupling with a coin as itpasses along the path thereby to produce a sensor signal to be comparedwith coin data for determining authenticity of the coin, the sensorsignal being of a value dependent upon characteristics which vary fromvalidator to validator, the method comprising: producing a calibrationvalue of the sensor signal for the validator to be calibrated as afunction of individual characteristics of the validator, by forming acalibration inductive coupling with the inductive sensor, providingensemble data concerning corresponding calibration values of the sensorsignal derived previously from an ensemble of other coin validators ofsaid design and sensor signals previously produced by the validators ofthe ensemble in response to a true coin of a particular denomination,comparing the calibration value of the sensor signal from the validatorto be calibrated with the ensemble data, and deriving for said validatorto be calibrated a value of the sensor signal for said coin denominationthat is compensated in respect of the individual characteristics of thevalidator, said ensemble data being configured as a database ofvalidator data sets derived from said ensemble of coin validators ofsaid design, each data set comprising the calibration value produced bya respective individual validator of the ensemble and a value of thesensor signal produced in response to a true coin of a particulardenomination by the individual validator.
 30. A method according toclaim 29 including selecting data from the data sets in dependence upona comparison of the sensor signal calibration value for the validatorbeing calibrated, with the corresponding calibration values of the datasets.
 31. A method according to claim 29 including forming from the datasets, a plurality of average values of the difference between thecalibration value of the sensor signal and the corresponding sensorvalue for the true coin, for the data sets in which the calibrationvalue of the sensor signal falls within predetermined respective rangesof values thereof.
 32. A method according to claim 31 includingtransmitting data concerning said ranges and the average values to thecoin validator to be calibrated, selecting one of said ranges bycomparing the calibration value of the sensor signal for the validatorbeing calibrated with said ranges, and combining said average value forthe selected range with the calibration value of the sensor signal forthe validator being calibrated whereby to provide the compensated valueof the sensor signal for the validator being calibrated.
 33. A methodaccording to claim 29 including associating upper and lower window limitvalues with the compensated value and storing the window limit values inthe validator being calibrated.
 34. A method according to claim 33wherein the transmitted data is fed from a central location to aplurality of validators to be calibrated at remote locations.
 35. Amethod according to claim 33 wherein the transmitted data is fed from acentral location to an individual validator to be calibrated at a remotelocation, in response to a request from the validator.